Accurate models of visual cortical function require a precise knowledge of how visual stimuli are represented within the cortex and the specific circuits that are involved in this representation. This knowledge is not only important to understand visual processing in the brain but it is also essential for the use of future cortical prosthesis that could provide vision to the blind through electrical microstimulation. Over the past years, there has been a great effort to investigate how line orientation and visual space are mapped within the primary visual cortex and how these representations are linked by different types of intracortical connections (horizontal connections, feedback connections and local intracortical connections). However, the equivalent measurements for geniculocortical connections are still missing. This gap in our knowledge is very significant because the geniculocortical connections are the main entrance of visual information to the brain and their functional organization is intimately related with the cortical representation of visual space. Lacking these data, current models of cortical function use very different patterns of geniculocortical connectivity, from those that assume a random distribution of the afferents to those that assume a neat alignment of the geniculate receptive fields along the preferred orientation of each cortical domain. In this proposal, we will use a new, powerful combination of multielectrode recording, optical imaging and neuronal tracer techniques to fill this important gap in knowledge and provide new experimental constraints to models of cortical function. Our experiments will reveal the organization of the geniculocortical pathway at the submillimeter scale and the role of this micro-organization in the representation of line orientation and visual space within the cortex. In addition, we will investigate the role of the geniculocortical pathway in the spontaneous activation of orientation domains in the absence of visual stimuli. The results of the proposed experiments will help to uncover mechanisms of cortical processing that could be used in the future to prevent and treat different forms of central visual disorders.